Collagen induced arthritis is an animal model for rheumatoid arthritis that shares a number of clinical, hematological, serological, and radiographic features with human disease. Type II collagen is a major component of articular hyalin cartilage and is a potential autoantigen in RA. Predisposition to RA has been linked to the MHC class II genes with haplotypes HLA-DQ8/DR4 showing the highest relative risk, and DQ6/DR2 being resistant. We generated transgenic mice expressing the above class II genes in the absence of endogenous class II molecules to generate a new humanized mouse model for rheumatoid arthritis restricted by human HLA class II molecules. Several interesting findings have emerged from our studies so far. In the current proposal, we will generate HLA-DQ transgenic mice expressing HLA-DQ4 and -DQ9 linked to RA in Asian and South American populations, and HLA-DR*O4O2 and *0404 which differ only in the HVR3 region residues to determine the role of the "shared epitope" in human RA. Double, triple, and quadruple transgenic mice will be generated to simulate human haplotypes to understand the interaction, gene complementation, and additive effect of multiple DQ/DR genes in the human disease. We will replace the mouse CD4 with human CD4 in these lines. Using knockout mice for CD4, CD8, and CD28, we will explore the role of costimulators in the disease process. We will identify the T cell and B cell specific epitopes on type II collagen, and look at the T cell repertoire and the TCR VB CDR3 usage. We will produce HLA class II tetramers in the context of human type II collagen peptides to identify specificity of collagen reactive T cells in the joints. Finally, using synthetic peptides and cyanogen bromide fragment of human type II collagen, we will explore various avenues of immunotherapy in the disease process. These studies should reveal the mechanism by which human HLA class II molecules predispose to human RA, and their role in the onset and severity of the disease. Thus, this humanized disease model for RA will have HLA class II, human CD4, and human type II collagen peptides as critical elements.